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KEY MESSAGES

- Hot Tuesday with a slight (level 2 of 5) risk for severe storms over the plains east of the Black Hills. Main hazards will be very large hail (2+") and damaging winds. A tornado or two may also be possible.

- Critical fire weather conditions will develop over northeastern WY tomorrow afternoon and evening. Further east, near critical to locally critical fire weather conditions are expected over portions of western SD and the Black Hills.

- Cooler Wednesday and Thursday

- Near daily chances for at least isolated showers/storms through the week.

UPDATE

Issued at 1047 PM MDT Mon Jun 8 2026

Lee cyclone will develop over western SD on Tuesday with attendant cold front/dry line pushing through the CWA through the day. Low level SW flow over northeastern WY will advect a hot and very dry airmass into the area with sfc dewpoints dropping into the upper 20s to low 30s while temperatures climb into the mid to upper 80s. This will support afternoon RH values as low as 10 to 15% across much of the area. Therefore have issued a Red Flag Warning for northeastern WY for the afternoon and evening.

Forecast remains on track for potential severe weather over the eastern tier of our CWA. 00z CAMs show line of storms developing along the cold front as it pushes across western SD. 00Z NAM now shows corridor of 3000-4000 J/kg ML CAPE east of the Black Hills with minimal capping. Bulk shear values of 30-40kt will support rotating updrafts and organized cells with hodographs showing low level curvature. This combined with steep 700-500mb lapse rates of 8- 9C/km will support a very large hail threat (2+") as well as damaging wind gusts and a low tornado risk. Storms may initially start off as discrete before transitioning to a linear mode as the front pushes through with damaging wind gusts being the main threat.

DISCUSSION

(This Evening Through Monday) Issued at 1256 PM MDT Mon Jun 8 2026

Current upper air models show upper low centered over AB/SK border, with upper ridge over the Great Lakes, and southwest flow over the forecast area. Surface analysis shows high pressure over the WY/SD border. Radar and Satellite show mostly clear skies, with some isolated showers over northwestern SD this afternoon. Winds are transitioning to the southeast as the high slides eastward, while temperatures currently sit in the 60s to low 70s.

Aside from these few isolated showers/storms this afternoon through tonight, expect most areas to remain dry. Tuesday is expected to be hotter, as low level WAA sets in, bringing highs from the mid 80s to nearing 100 Tuesday afternoon, with the warmest temperatures expected in the western SD plains. Main concern for Tuesday will be increasing chances for storms throughout the day. Plenty of available energy Tuesday, with models showing CAPE values ranging from 2500-3500 j/Kg for areas east of the Black Hills. With steepening lapse rates (8-9 c/km) and 0-6km shear in the 35-45kt range, some severe storms may be possible. Currently CAMS show some potential for isolated supercell development late afternoon, but severe chances increase later as LLJ increases and models show storm mode switching to more linear storms forming along the frontal boundary as it moves through. Timing will be important, as currently models show isolated storms developing around 3pm MDT and over the next couple hours forming along the front, however by then models have the boundary almost out of our area. This should limit the severe threat to areas east of the Black Hills closer towards central SD. Some of our western SD plains are in a marginal to slight risk for severe storms, while the enhanced risk remains just east of our forecast area.

Following this cold front, low level northwest flow will usher in a bit cooler temperatures for Wednesday and Thursday, with highs ranging from the mid 60s to low 80s. Chances for isolated to scattered showers/storms will continue mid-week as a weak wave moves through Wednesday, and slightly strong wave on Thursday, though currently severe storms are not expected those days. By Friday, the upper low now sits over Ontario, with a more quasi- zonal flow over the forecast area and brief break from isolated precipitation. Models do show another disturbance moving through over the weekend, bringing precipitation chances back later Saturday into Sunday.

AVIATION

(For the 06Z TAFS Through 06Z Tuesday Night) Issued At 1047 PM MDT Mon Jun 8 2026

VFR conditions are expected throughout the forecast period. Showers and thunderstorms are expected Tuesday afternoon (mainly western SD) and will push eastward through the evening. MVFR conditions and gusty, erratic winds are expected with any storms. Southerly winds will continue overnight, then become southwesterly through the day Tuesday, with gusts to 35-40kt at times.

FIRE WEATHER

Issued At 1046 PM MDT Mon Jun 8 2026

Widespread critical fire weather conditions expected to develop over northeastern WY tomorrow afternoon. Afternoon humidities will drop to 10 to 15% with southwest winds of 20 to 30 mph, gusting up to 40 mph. A few isolated thunderstorms can't be ruled out in the afternoon, these storms will be high based and capable of gusty, erratic winds and lightning. These storms may be accompanied by little to no precip. Because of the hot, dry, and windy conditions and dry fuels, have opted to issue a Red Flag Warning for much of the northeastern WY plains for tomorrow afternoon.

Further east, near critical to locally critical fire wx conditions may develop over southwestern SD, the Black Hills and adjacent plains. Humidities will drop to 10 to 20% in these areas with afternoon temperatures climbing into the mid to upper 90s. Southwest winds of 20 to 30 mph with gusts of up to 40 mph are also expected. Confidence in critical fire weather conditions developing are lower over western SD due to recent rainfall and greening fuels, therefore have held off on issuing any Red Flag Warnings over our SD zones.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...Red Flag Warning from 11 AM to 8 PM MDT Tuesday for WYZ314-315- 317.